Synthetic linear polyamides



Patented Feb. 12, 1952 SYNTHETIC LINEAR POLYAMIDES Donald Cargill Peaseand Carleton Thomas Handy, Wilmington, Del., assignors to E. I. do. Pontde Nemours & Company, Wilmington, Del., a corporation of Delaware NoDrawing. Application March 25, 1950, Serial No. 152,006

3 Claims. (Cl. 26078) This invention relates to synthetic linearpolyamides and, more particularly, to a new synthetic linear polyamideof the nylon type which has superior fiber and bristle properties, andto the process of preparing same.

Synthetic linear polyamides have achieved considerable importance asfibers for use in textiles. They have also found utility in bristleapplications. The polyamides which have achieved importance in theseuses are of the general types described in U. 8. Patents 2,071,250,2,071,253 and 2,130,948 and can be obtained by self-polymerization of amonoaminocarboxylic acid, by reacting a diamine with a dibasiccarboxylic acid in substantially equimolecular amounts, or by reacting amonoaminomonohydric alcohol witha dibasic carboxylic acid insubstantially equimolecular amounts. In place of the acids, amines, andalcohols, equivalent amide-forming derivatives may be used. Thepolyamides obtained have an intrinsic viscosity of at least 0.4. Onhydrolysis with hydrochloric acid, the amino acid polymers yield theamino acid hydrochloride, the diaminedibasic acid polymers yield thediamine hydrochloride and the dibasic carboxylic acid, and the aminoalcohol-dibasic acid polymers yield the amino alcohol hydrochloride andthe dibasic carboxylic acid.

of the polyamides, those that have achieved commercial importance forfiber applications in view of their superior properties, e. g., heatsetting properties, are usually opaque, generally have an intrinsicviscosity considerably exceeding 0.4 and, usually, 0.8 or higher, andwithstand ironing temperatures but melt without decomposition underspinning conditions, e. g., at 225-300 C. To obtain these preferredproperties in polyamides, it is generally desirable to start withdibasic carboxylic acids and diamines which have at least 6 carbonsseparating the carboxylic hydroxyl and amine groups.

An object of the present invention is to provide a new synthetic linearpolyamide and a process for preparing same. A further object is toprovlde such a polyamide having an intrinsic viscosity of at least 0.8and a desirable softening point sufllciently high for ironing andtextile handling operations but below the decomposition point of thepolyamide. A more particular object is to provide such a polyamidegiving oriented films and fibers having exceptionally low shrinkage inboiling water, and bristles characterized by superior stillness and ahigh rate of recovery from a sharp bend. other objects will be apparent50%l0% of a normally liquid mixture of stereotermedbis(4-aminocyclohexyl) isomers of di(p-aminocyclohexyl) methane, with asubstantially equimolecular proportion of glutaric acid, underpolyamide-forming conditions, e. g., heating, preferably under pressureat first and then followed by vacuum heating at 200 C.-300 C. In thismanner a new synthetic linear polyamide is obtained having an intrinsicviscosity of at least 0.8, and which melts within the range of 260C.-290 C. and is characterized by unexpected superiority in the lowshrinkage in boiling water of oriented articles made therefrom, and theresilience and rapid recovery from sharp bends of fibers, bristles, andthe like made therefrom.

Di(p-aminocyclohexyl) methane is a diamine having the followingstructural formula:

from which it can be seen that stereoisomers arise from the differentpossible relationships of the bonds of the carbons attached to thebridge methylene and the carbons attached to the amino groups withrespect to the cyclohexyl ring (1. e., the cis and trans configurationsof the carbonhydrogen bonds of those carbons in the above formula whichhave only one hydrogen). The three expected isomers diii'er in physicalproperties, particularly in melting points. The above diamine isobtained as a mixture of isomers by hydrogenation of di (p-aminophenyl)methane. This latter compound results from the reaction of formaldehydewith aniline. Depending upon the choice of conditions for thehydrogenation either a mixture of stereoisomers is obtained that isliquid at 25 0., i. e., normally liquid, or a mixture is' obtained thatis solid at 25 C., i. e., normally solid, the latter mixture generallymelting above C.

.The preparation and properties of the normally solid mixture ofstereoisomers of di(paminocyclohexyl) methane, equally correctlymethane, are fully disclosed in U. S. Patent 2,494,563. The preparationand properties of the normally liquid mixture of stereoisomers ofdi(p-amniocyclo- 3 hexyllmethane are fully disclosed in U. B.application Serial No. 98,174, filed June 9, 1949 in the name of G. M.Whitman and assigned to the assignee of the instant application. Ingeneral, the preparation of normally liquid mixtures of stereoisomers isfavored by the use of a ruthenium hydrogenation catalyst at relativelylow temperatures whereas higher temperatures and other hydrogenationcatalysts favor the production of the higher melting normally solidmixtures of stereoisomers of di(p-aminocyclohexyl) methane.

The properties of the new polyamide of this invention are quiteunexpected and were unpredictable. While glutaric acid has beendisclosed as a polyamide-forming acid, di(p-a.minocyclohexyDmethane isthe only primary aliphatic diamine. so far as applicants are aware, withwhich glutaric acid reacts to give high molecular weight spinnablenylons, i. e., a polyamide having an intrinsic viscosity of at least0.8. A normally liquid mixture of stereoisomers of di(p-aminocyclohexyl)methane when reacted with glutaric, adipic, or sebacic acids, gives aclear polymer which softens at about 200-235 C. and has excellentmolding properties. When a normally solid mixture of the stereoisomersis used instead of a normally liquid mixture, an opaque polyamideresults with glutaric and adipic acids which is too high melting for usein conventional spinning equipment. Further, although polyamide fibersprepared from glutaric, adipic, or sebacic acid with the normally liquidmixture of stereoisomers can be fabricated for use in fabric and bristleapplications, these oriented products have considerable shrinkage, above50%, in boiling water and do not readily respond satisfactorily tosetting treatments. As shown more particularly in Example 11hereinafter, the bristle properties of these polyamide fibers arematerially less favorable than those of oriented filaments of thepolyamide of the present invention with respect to both recovery fromsharp bending and water sensitivity.

Thus, neither the experience of the prior art with glutaric acid as apolyamide-forming acid nor the properties of polyamides formed by thereaction of glutaric, adipic, or sebacic acids with either a normallysolid or a normally liquid mixture of stereoisomers ofdi(p-aminocyclohexyl) methane would forecast the properties of thepolyamide of this invention.

The following examples in which the parts are by weight unless otherwisestated, illustrate specific embodiments of the invention.

Example I To a glass lined pressure resistant vessel was added 52.86parts glutaric acid, 50 parts of phenol and 84.18 parts ofdi(p-aminocyclohexyl)methane comprising a mixture of the solid andliquid mixtures of isomers in the ratio of 4: 1. The vessel wasevacuated and pressured with nitrogen 3 times. It was evacuated to apressure of 5 mm. of mercury, sealed and heated -for one hour at 210 C.The vessel was then opened, heated at 285 C. for one hour under anatmospheric pressure of nitrogen and at 306 C. for hour at a pressure of5 mm. of mercury. The polymer thus formed had an intrinsic viscosity of0.83. A film mil thick was melt pressed at 600 lb./sq. in. at atemperature of 270 C. Narrow foils were drawn at a ratio of 3/1 in waterat 100 C. These drawn foils shrank only 5% in water at 100 C. Bycontrast, drawn foils prepared similarly from the adipic acid Po ym r ofthe liquid mixture 01 4 isomers of bis(p aminocyclohexylimethane shrank53%.-

E'scmple II A glutaric acid polyamide of di(p-aminocyclohexylimethanecomprising the solid and liquid mixtures of isomers in the ratio of85:15 was prepared as described in Example I. The polyamide had anintrinsic viscosity of 0.86. am 20 mil thick was melt pressed at atemperature of 270 C. Bristle was prepared by melt extruding a 24 milfilament at 290 0., drawing in mineral oil at 125 C. at a ratio of3.2:1, and setting in water at 100 C. while wrapped on a form to preventshrinkage. Recovery from bending was measured by wrapping 10 turns ofthe bristle around a 00 milmandrelandmaintainingthebristiethere for 4minutes. The bristle was instantly released by cutting one end andallowed to recover in water. Rate of recovery for this bristle was muchfaster than for bristle from the sebaclc acid polyamide ofhexamethylenediamine, a commercial nylon bristle. Thus, after cuttingfrom the 90 mil mandrel the subject bristle recovered all but 9% of thebending in 30 seconds and all but 7.5% in 60 seconds with all but 3%recovered in one hour. Bristle from the sebacic acid polyamide ofhexamethylenediamine recovered all but 15% in 30 seconds and all but 13%in one minute with all but 4% recovered in one hour. The modulus ofelasticity, a measure of the stiffness. for the subject bristle was alsohigher, being 600,000 lb./sq. in. at 25 C. and 50% relative humidity,and 547,000 lb./sq. in. at 25 C. and 100% relative humidity comparedwith 480,000 lb./sq. in. at 25 C. and 50% relative humidity, and 280,000lb./sq. in. at 25 C. and 100% relative humidity forpolyhexamethylenesebacamide.

The above comparison of fiber properties this invention as compared tothe properties of a typical straight chain aliphatic polyamide.Unexpectedly, the superiority of the instant polyamide is also verydefinite in comparison to the properties of the polyamide resulting fromthe reaction of the normally liquid mixture ofdi(paminocyclohexyDmethane with adipic acid. Thus with the adipic acidpolyamide, bending as described above resulted in the relatively highnon-recovery of 15% in an hour. The modulus of elasticity for the adipicacid polyamide was 450,000 lb./sq. in. at 25 C. and relative humidity.

Example III An autoclave was charged with 17.5 parts of the preformedglutaric acid salt of a solid mixture of stereoisomers ofdi(p-aminocyclohexyl)- methane, 7.5 parts of the corresponding preformedglutaric acid salt of a liquid mixture of the stereoisomers, and 0.002part of Dow Corning Anti-foam A, an organo-silicon oxide polymer. Thismixture was fiushed with nitrogen and heated for one hour at 204 C.under a Pressure of 240 lb./sq. in., followed by heating at 282 C. fortwo hours at atmospheric pressure and at 284 C. for one hour at 5 mm. ofpressure. The polyamide thus obtained had an intrinsic viscosity of 0.91and a softening temperature of 265 C.- 270 C. Oriented fibers after heatsetting had a work recovery at 1% elongation of 81, a shrinkage of 7% inboiling water, and a modulus of 42 g./denier and a wet modulus of 29g./denier. By comparison, polyhexamethyleneadipamide had a modulus of 29g./denier and a wet modulus of 10 g./denier.

This example serves to illustrate the equivalency of adding thepreformed glutaric acid salt of a solid mixture of stereoisomers ofdi(aminocyclohexyDmethane and the preformed glutaric acid salt of aliquid mixture of the stereoisomers to the reaction vessel as contrastedto adding the separate components forming the salts and then forming thesalts in situ, the procedure of Examples I and II. While one proceduremay be more convenient than the other depending on circumstances, theparticular procedure used has no influence on the polyamide formed.

The salt of glutaric acid with either the solid or liquid mixture ofstereoisomers may be readily prepared, e. g., by mixing separate alcoholsolutions of glutaric acid and the mixture of stereoisomers, followed byisolation of the salt which is then condensed to the polyamide by heat,generally at 200 C.-300 C.

It will be understood that the above examples are merely illustrativeand that the present invention broadly comprises a linear polyamidehaving an intrinsic viscosity of at least 0.8, the polyamide being thereaction product of a, diamine mixture consisting, by weight, of 50%-90% of a normally solid mixture of stereoisomers ofdi(p-amino-cyclohexyl)methane and 50%- of a normally liquid mixture ofstereoisomers of di(p-aminocyclohexyl) methane, with a substantiallyequimolecular proportion of glutaric acid.

To obtain the linear polyamide as herein described requires that amixture be used of a normally solid mixture of the stereoisomers of di-(p-aminocyclohexyl) methane and a normally liquid mixture of thestereoisomers within the proportion range recited. It is preferred inorder to obtain a polyamide of optimum properties that the normallyliquid mixture of stereoisomers amount to %-30% of the composite mixtureconsisting of the liquid and solid mixtures of stereoisomers. Thepolyamide has an intrinsic viscosity of at least 0.8 and melts withinthe range of 260 C.-290 C. without decomposition.

Hydrolysis of the polyamide with hydrochloric acid results in theproduction of lutaricacid and di(p-aminocyclohexyl) methanehydrochloride.

The unexpected and particularly outstanding properties of the polyamideof this invention are the following: (1) The low shrinkage of orientedfilms and fibers in boiling water. This shrinkage is about 7% whereassimilar yarns prepared from polyamides of the liquid mixture ofstereoisomers of di(p-aminocyclohexyl) methane and glutaric, adipic, orsebaoic acid, all shrink more than 50% in boiling water and do notrespond easily to setting treatments. (2) The particularly desirablesoftening point (260290 C.) which is sufliciently high for ironing andtextile handling operations and below the decomposition point of thepolyamide. In contrast to this, the polyamide from glutaric acid and thesolid mixture of stereoisomers of the diamine does not fuse below 300 C.and is diillcult to spin, whereas the glutaric acid polymer from theliquid mixture of stereoisomers melts at about 200 C. (3) The superiorstiffness as compared to available polyamides as shown in Example II.(4) The high rate of recovery from a sharp bend exhibited by thepolyamides of this invention which is of outstanding utility in bristleapplications. As shown by the data in the examples the rate of recoveryfrom sharp bends is rapid and substantially complete.

The products of this invention may be used in various fiberapplications, however, their superior resiliency is most important inbristle applications. Their relative insensitivity to water is offurther utility in various brush uses where the bristle is subjected tomoisture.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

The invention claimed is:

1. A linear polyamide having an intrinsic viscosity of at least 0.8,said polyamide being the reaction product of a diamine mixtureconsisting. by weight, of 50%-90% of a solid mixture of stereoisomers ofdi(p-aminocyclohexyl)methane, said mixture melting above C., and %-10%of a liquid mixture of stereoisomers of di(paminocyclohexyl) methane,said mixture being liquid at 25 C., with a substantially equimolecularproportion of glutaric acid.

2. A linear polyamide having an intrinsic viscosity of at least 0.8,said polyamide being the reaction product of a diamine mixtureconsisting, by. weight. of '70%-85% of a solid mixture of stereoisomersof di(p-aminooyclohexyl)methane, said mixture melting above 40 C., and30 15% of a liquid mixture of stereoisomers of di- (p-aminocyclohexyl)methane, said mixture being liquid at 25 C., with a substantiallyequimolecular proportion of glutaric acid.

3. An oriented filament of the polyamide recited in claim 1.

DONALD CARGILL PEASE. CARLETON THOMAS HANDY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,130,948 Carothers Sept. 20,1938 2,252,554 Carothers Aug. 12, 1941 2,512,606 Bolton June 27, 1950FOREIGN PATENTS Number Country Date 67,203 Norway Dec. 20, 1943 OTHERREFERENCES Ser. No. 392,812, Kroeper et al. (A. P. C.) published Apr.20. 1943.

De Bell et al., Berman Plastics Practice, 1948 p. 289.

1. A LINEAR POLYAMIDE HAVING AN INTRINSIC VISCOSITY OF AT LEAST 0.8,SAID POLYAMIDE BEING THE REACTION PRODUCT OF A DIAMINE MIXTURECONSISTING BY WEIGHT, OF 50%-90% OF A SOLID MIXTURE OF STEREOISOMERS OFDI(P-AMINOCYCLOHEXYL) METHANE, SAID MIXTURE MELTING ABOVE 40* C., AND50%-10% OF A LIQUID MIXTURE OF STEREISOMERS OFDI(PAMINOCYCLOHEXYL)METHANE, SAID MIXTURE BEING LIQUID AT 25* C., WITH ASUBSTANTIALLY EQUIMOLECULAR PROPORTION OF GLUTARIC ACID.